Current mobile applications are generally built on a three-tier architecture consisting of a database server (a data tier), an application server (a logic tier), and a client or front-end system (a presentation tier). The various tiers are generally developed and maintained as independent modules, often on separate platforms. The client provides the user interface of the application, which is used to translate tasks and results to information the user can understand, as well as to allow users to submit instructions to the logic and data tiers. The logic tier coordinates the application, processes commands, and makes logical decisions and evaluations, and performs calculations, as well as moving data between the presentation tier and the data tier. The data tier stores and retrieves data and other information from a database or other file system. The information is passed to the logic tier for processing, and then back to the user for consumption.
Database management systems (DBMS) are software packages with computer programs that control the creation, maintenance, and use of a database. They allow organizations to conveniently develop databases for various applications. A database is an integrated collection of data records, files, and other objects. A DBMS allows different user application programs to concurrently access the same database. A DBMS provides facilities for controlling data access, enforcing data integrity, managing concurrency control, and recovering the database after failures and restoring it from backup files, as well as maintaining database security.
An in-memory database is a DBMS that primarily relies on main memory for computer data storage. It is contrasted with DBMSs which employ a disk storage mechanism. Main memory databases are faster than disk-optimized databases since the internal optimization algorithms are simpler and execute fewer CPU instructions. Accessing data in memory reduces the I/O reading activity when querying the data, which provides faster and more predictable performance than disk.